Level-Temp Control Relay SPST-Normally OpenLevel Temp Controller, SPST Normally Open, Heat Cool, Conduit Hub or Screw Mount, Input Voltage: 240V AC, 0. 2 Amp, SPST, Normally Open, Temperature Range: 20 to +140F. For use with 2 Wire, 24V Thermostats. These Level Temp controls have been designed to operate with a White Rodgers low voltage electric heat thermostat to provide a system for controlling electric warm air heaters and electric radiant heating devices such as duct heaters, wall heaters,